1. Field of the Invention
The present invention relates to a transmitting system utilized in a small-sized vehicle such as a motorcycle, a four-wheel buggy and the like, and particularly, to an improvement in a transmitting system utilized in a small-sized vehicle, in which a crankshaft of an engine and an input shaft of a multi-stage transmission, which is disposed in parallel to the crankshaft, are connected to each other through a fluid transmitting means including a pump impeller leading to the engine, and a turbine impeller leading to the multi-stage transmission.
2. Description of the Related Art
There are such already known transmitting systems for small-sized vehicles, in which the fluid transmitting means is comprised of a torque converter, as disclosed in, for example, Japanese Patent Application Laid-open No. 57-69163.
In such known transmitting system, as described in the above Publication, the crankshaft of the engine and the input shaft of the multi-stage transmission are connected to each other only through the torque converter, so that a torque shock generated at the time of the starting the vehicle or during shifting is absorbed by a slipping action of the torque converter.
However, the known transmitting system suffers from the following drawbacks: The torque converter or the fluid coupling has a slipping function, but performs the transmission of a torque to certain degree, as long as a power is input from the engine to the torque converter or the fluid coupling. Therefore, in the known system, at the time of starting the vehicle in which the transmission is switched over from a neutral position to a low or first-speed position, a creep phenomenon is produced in which power is transmitted to a driving wheel of the vehicle to certain degree, even if the engine is in an idling state. During traveling of the vehicle, the friction always occurs in switching and sliding portions of the transmission due to the transmitted torque. For this reason, there are inconveniences that the resistance to the switching of the transmission is large, and a large shifting load is required. In addition, the torque converter is mounted to the input shaft of the multi-stage transmission driven in a decelerated manner from the engine and for this reason, the transmitted torque borne by the torque converter is relatively large, and hence, a large-sized torque converter having a large capacity is obliged to be used. This makes it difficult to provide the compactness of the power unit including the engine and the transmission.
Accordingly, it is an object of the present invention to provide a transmitting system of the above-described type for a small-sized vehicle, wherein the creep phenomenon is eliminated, and the shifting operation of the transmission can be carried out lightly, and moreover, the compactness of the power unit can be obtained.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a transmitting system for a small-sized vehicle in which a crankshaft of an engine and an input shaft of a multi-stage transmission, which is disposed in parallel to the crankshaft, are connected to each other through a fluid transmitting means including a pump impeller leading to the engine, and a turbine impeller leading to the multi-stage transmission, wherein the transmitting system includes a shifting clutch, the fluid transmitting means and the shifting clutch being mounted on the crankshaft of the engine and connected in series to each other, one of the fluid transmitting means and the shifting clutch being connected to the crankshaft, and the other being connected to the input shaft of the multi-stage transmission through a primary reducing device.
The fluid transmitting means corresponds to a torque converter T, Txe2x80x2 in embodiments of the present invention which will be described hereinafter.
With the first feature, during idling of the engine, the transmitting of power to the shifting clutch and the like can be cut off by controlling the shifting clutch to its OFF state irrespective of the presence of the fluid transmitting means, even in a first-speed position of the transmission, thereby preventing the creep phenomenon. During shifting, the transmission can be brought into an unloaded state by first controlling the shifting clutch to its OFF state irrespective of the presence of the fluid transmitting means, thereby conducting the shifting lightly without generation of a torque shock.
Moreover, the crankshaft is rotated at higher speed than that of the input shaft of the transmission which is driven through the reducing device. Therefore, the transmitted torque borne by the fluid transmitting means and the shifting clutch mounted to the crankshaft is relatively small, and the capacities of the fluid transmitting means and the shifting clutch can be reduced correspondingly, leading to the compactness of the fluid transmitting means and the shifting clutch. Therefore, the compactness of the power unit can be provided, despite the disposition of both the fluid transmitting means and the shifting clutch.
According to a second aspect and feature of the present invention, in addition to the first feature, the primary reducing device, the fluid transmitting means and the shifting clutch are disposed on the crankshaft of the engine in the named order from one sidewall of a crankcase supporting the crankshaft with a bearing interposed therebetween toward the outside.
With the second feature, the primary reducing device is disposed nearest to the sidewall of the crankcase and hence, the flexing moment applied to the crankshaft and the input shaft of the transmission with the operation of the primary reducing device can be minimized. The fluid transmitting means is larger in weight than the shifting clutch, but is disposed nearer to the sidewall of the crankcase than the shifting clutch and hence, the flexing moment applied to the crankshaft due to their weights can also be minimized. As a result, the foregoing can contribute to an enhancement in durability of the crankshaft, the input shaft of the transmission and the bearings supporting them, in cooperation with the compactness of the fluid transmitting means and the shifting clutch.
According to a third aspect and feature of the present invention, in addition to the second feature, a valve-operating timing transmitting device is mounted on the crankshaft on a side opposite to the primary reducing device, the fluid transmitting means and the shifting clutch, with an internal chamber in the crankcase of the engine sandwiched therebetween.
With the third feature, the disposition of the primary reducing device at the location near to the sidewall of the crankcase can be achieved without any interference by the timing transmitting device. Therefore, when the primary reducing device is in operation, the flexing moment exerted to the crankshaft and the input shaft of the transmission can be suppressed to a small level to ensure the durability of the crankshaft, the input shaft of the transmission and the bearings supporting them.
According to a fourth aspect and feature of the present invention, in addition to the second feature, a generator is mounted on the crankshaft on a side opposite to the primary reducing device, the fluid transmitting means and the shifting clutch, with an internal chamber in the crankcase of the engine sandwiched therebetween.
With the fourth feature, the group of the primary reducing device, the torque converter and the shifting clutch, and the group consisting of only the generator having a relatively large weight are disposed on the opposite sides of the crankshaft and hence, the lateral distribution of the weight of the power unit can be equalized. Moreover, since the generator and the fluid transmitting means are disposed coaxially on the crankshaft, the turning vibration generated on the generator can be absorbed by the fluid transmitting means, which can contribute to the quietness of e power unit.